1. Field of the Invention
The invention relates to an apparatus for controlling or regulating a web property profile of a paper or cardboard web in the manufacturing process of a paper or cardboard web manufacturing machine, and to a process for controlling or regulating a web property profile of a paper or cardboard web in the manufacturing process of a paper or cardboard web manufacturing machine.
2. Discussion of Background Information
Many interfering factors occur in the production of a paper or cardboard web during the manufacturing process, which can negatively impact the web properties of the paper or cardboard web with respect to its uniformity across the machine width as well as with respect to its stability during the manufacturing process. Temperature variations, pressure variations, work tolerances, and errors in the construction or the adjustment of the paper or cardboard manufacturing machine during the manufacturing process are, for example, some of these interfering factors. The main web properties which influence the quality of the produced paper or cardboard are the mass per unit area, the fiber orientation, and formation. However, properties such as ash content, opacity, moisture content, web thickness, and roughness of the web play a significant role as the quality criteria of a paper or cardboard web. In general one tries to keep the above-mentioned web properties as uniform and constant as possible across the entire width and over the entire length of the web.
Patent document DE 35 35 849 suggests changing the width of outlet opening of a headbox at certain locations of the web width such that, correspondingly, the throughput of the material suspension is changed locally. If the throughput of the material suspension changes locally with a concentration that is uniform across the machine width, it will have an effect on the amount of solid matter deposited at this location of the web. Thus, an adjustment of the mass per unit area cross-sectional profile can be attained.
Another patent document DE 40 19 593, discloses a device and a process for regulating the weight per unit area profile of the web surface. The concentration of the material suspension flow here is to be changed at a particular location of the web width if the weight per unit area profile of the paper or cardboard web deviates. In order to achieve this, it is suggested that the headbox be sectioned at least partially across the machine width and that it is fed with the assistance of individually controlled sectional flows exhibiting individually adjustable concentrations. The individual concentration adjustment of each respective sectional flow occurs by regulating the feed proportions of two individual flows with a constant but different concentration. Due to the different sectional flow compositions with respect to fibrous material, ash, and other additives, a change in the weight per unit area results in the corresponding location of the web width.
In the control process, the weight per unit area cross-sectional profile of the paper or cardboard web is measured at the end of the paper or cardboard machine and the feed flow proportions of the two individual flows of different concentration, which form the respective sectional flow, are regulated with a control loop such that the most uniform weight per unit area cross-sectional profile is provided.
A similar control/regulator device, as well as a process to regulate the weight per unit area cross-section and the fiber-orientation cross-sectional profile is known from the patent document DE 42 39 845. This document, likewise, proposes to construct the headbox at least partially in sections and to control the paper or cardboard material suspension in the individual sections with respect to its consistency and/or fiber orientation by admixing diluting water or other fluids in order to regulate the respective cross-sectional profile. A similar sectional headbox is known from the patent document DE 43 16 054.
Patent document DE 196 34 997 describes a control device with several measuring sensors and a process to regulate different web property profiles. Likewise, patent document DE 196 34 996 discloses a headbox that regulates the pulp density with a paper or cardboard pulp consistency regulator.
In patent documents DE 42 11 291 and DE 42 11 290, a sectional consistency regulator of a headbox is depicted, exhibiting a single valve for each section with a constant volumetric flow. In the patent documents DE 40 19 593 and DE 41 12 347, a material consistency regulator and volumetric flow regulator for a sectioned headbox, each exhibiting two valves, is shown.
The disclosure of each of the foregoing patent documents is expressly incorporated by reference herein in their entirety.